Holdings of New GM Securities at March 31, 2015 - Holdings of Securities for Trust Beneficiaries (Detail) - Liquidation Basis of Accounting [Member] $ in Thousands	Mar. 31, 2015 USD ($) shares
Summary of Investment Holdings [Line Items]
Fair Value	$ 917,977
New GM Common Stock [Member]
Summary of Investment Holdings [Line Items]
Number | shares	11,390,701
Fair Value	$ 427,151
New GM Series A Warrants [Member]
Summary of Investment Holdings [Line Items]
Number | shares	10,354,971
Fair Value	$ 287,351
New GM Series B Warrants [Member]
Summary of Investment Holdings [Line Items]
Number | shares	10,354,971
Fair Value	$ 203,475